The Confederated Tribe of Goshutes and two conservation organizations filed notice Wednesday that they plan to sue the Interior Department for not responding to a petition to put a rare Utah fish on the federal list of threatened or endangered species.

The least chub, a small minnow found only in Utah's Bonneville Basin, now lives in just six fragile wild populations, three in the Snake Valley.

Along with the tribe, the Great Basin chapter of Trout Unlimited and Wild Utah Project claim the Southern Nevada Water Authority's plans to tap Snake Valley groundwater to feed Las Vegas growth threatens the least chub's survival.

The groups filed their petition to protect the fish in June 2007. Under the Endangered Species Act, federal officials should have responded with a finding of whether the petition's claims were sufficient to warrant further consideration within 90 days. A decision on whether to list the fish then should have come within a year.

"The least chub is an ambassador from an imperiled ecosystem - desert springs in western Utah," Rupert Steele of the Goshute Reservation said in a statement. "If we can save this fish, we know we will have protected an ecosystem and the people whose lives depend on it for future generations."

Southern Nevada wants to siphon 25,000 to 50,000 acre-feet a year of groundwater and ship it via a pipeline to Las Vegas, 250 miles to the south. Proponents say without the water, southern Nevada's economy will wilt.

Critics warn the project would cause underground water levels to drop too low for desert vegetation to survive. If the plants die, they add, nothing will hold the soil in place, and dust storms will hit the Wasatch Front, which already has air pollution.